One known resistor of this type is disclosed in Japanese Laid-open Patent No. H4-102302.
The conventional resistor and its manufacturing method are described below with reference to drawings.
FIG. 53 is a section view of this conventional resistor.
In FIG. 53, discrete substrate 1 made of ceramic such as alumina has insulation resistance. A pair of first upper electrode layers is provided on both left and right ends of the top face of discrete substrate 1. Resistor layer 3 is provided on the top face of discrete substrate 1 such that a part of resistor layer 3 overlaps the pair of first top electrode layers 2. First protective layer 4 is provided such as to cover only and all resistor layer 3. Trimming groove 5 is created on resistor layer 3 and first protective layer 4 for adjusting a resistance. Second protective layer 6 is provided only on the top face of first protective layer 4. A pair of second top electrode layers 7 is provided on the top face of the pair of first top electrode layers 2 such that second top electrode layers 7 extend fully to the width of substrate strip 1. A pair of side electrode layers 8 is provided on both side faces of discrete substrate 1. A pair of nickel-plated layers 9 and a pair of solder-plated layers 10 are provided on the surface of the pair of second top electrode layers 7 and the pair of side electrode layers 8. Solder-plated layers 10 are at a lower level than second protective layer 6.
A method for manufacturing the conventional resistor as configured above is described next with reference to drawings.
FIGS. 54(a) to 54(f) are process charts illustrating how to manufacture the conventional resistor.
As shown in FIG. 54(a), the pair of first top electrode layers 2 is applied on both left and right ends of the top face of discrete substrate 1 having insulation resistance.
Then, as shown in FIG. 54(b), resistor layer 3 is applied on the top face of discrete substrate 1 such that a part of resistor layer 3 is overlaid on the pair of first top electrode layers 2.
Next, as shown in FIG. 54(c), first protective layer 4 is applied so as to cover only and all resistor layer 3, and then trimming groove 5 is created on resistor layer 3 and first protective layer 4, typically using a laser, such that the total resistance at resistor layer 3 falls into a predetermined resistance range.
Then, as shown in FIG. 54(d), second protective layer 6 is applied only on the top face of first protective layer 4.
As shown in FIG. 54(e), the pair of second top electrode layers 7 is applied to the top face of the pair of first top electrode layers 2 to fully cover the width of substrate strip 1.
As shown in FIG. 54(f), the pair of side electrode layers 8 is applied to the pair of first top electrode layers 2 and both left and right side faces of discrete substrates 1 such that side electrode layer 8 are electrically coupled to the pair of first and second top electrode layers 2 and 7.
Lastly, the surfaces of the pair of second top electrode layers 7 and the pair of side electrode layers 8 are nickel plated, and then soldered to form a pair of nickel-plated layers and a pair of solder-plated layers 10 to complete the conventional resistor.
The above resistor has been radically downsized, and a very small resistor of L 0.6 mm×W 0.3 mm×T 0.25 mm is currently being manufactured.
Problems with the above conventional configuration and method in manufacturing a very small resistor of L 0.6 mm×W 0.3 mm×T 0.25 mm are described next.
In the conventional insulated substrate sheet made of ceramic such as alumina, a substrate-splitting groove is created on the insulated substrate sheet before baking; the substrate is then baked to form the insulated substrate sheet. Accordingly, the substrate-splitting groove previously made on the insulated substrate sheet may have variations in its dimensions due to minute variations in the composition of the insulated substrate sheet and minute variations in the baking temperature of the insulated substrate sheet. (These dimensional variations may reach about 0.5 mm in an insulated substrate sheet of about 100 mm×100 mm.) When an extremely fine resistor is manufactured using an insulated substrate sheet having such dimensional variations, the dimensions of each substrate need to be classified lengthwise and widthwise into extremely minute dimensional ranks, and screen printing masks corresponding to each dimensional rank need to be prepared for top electrode layer 2, resistor layer 3, and first protective layer 4. In addition, individual masks need to be used so as to match the dimensional rank of each substrate. As a result, the manufacturing process becomes very complicated. (If the dimensions in horizontal and vertical directions are classified in 0.05 mm steps, there will be 25 ranks widthwise and lengthwise respectively, resulting in about 600 ranks in total for lengthwise and widthwise classification.)
The present invention aims to solve the above problem by eliminating the need for dimensional classifications of substrates. Accordingly, one step, that of replacing a mask according to the dimensional rank of the substrate required in the prior art, may be eliminated, offering an inexpensive fine resistor.